Plasma treatments are widely used, for example to activate surfaces for a better adhesion, for the sterilization of food, wounds or surgical cutlery, for coating or even to the in situ production of ozone from precursor gases. Especially the industrial field of application of plasma treatment extends to new special applications. Increasingly, non-plasma-based standard processes are replaced by plasma processes. The requirements on the plasma may vary from application to application regarding the plasma properties (such as plasma pressure, plasma power, plasma density, plasma temperature or degree of ionization) or the design of the plasma generator. Cost efficiency and at the same time variable applicable concepts are drivers for standardized plasma generators. Desirable properties are in particular a compact, flexible design of the plasma generator, low voltage operation to atmospheric pressure and a lower excess heat during the plasma generation. Plasma sources with a nozzle shaped structure can produce plasma beams with a relatively high ion density. However, as a wide surface machining of components is only possible by scanning the plasma beam across the surface. At a given power density of plasma generator the processing time increases with the area to be treated. In case an increased number of plasma generators is simultaneously used the overhead for the electrical wiring and supplies with process gas increases as well.
The German patent application DE 37 33 492 A1 discloses a device with an electrically powered plasma generator. Two electrodes form an air gap, through which a gas stream is conducted. With the help of a corona discharge the streaming gas is ionized.
The UK patent application GB 1 412 300 A reveals an arc generator with a plurality of electrodes to which an at least three-phase AC voltage is applied in order to ignite plasma beam from a gas and to direct the plasma beam onto a work piece which is at ground potential. In accordance with one embodiment, the three electrodes reach into a gas flowed trough housing with a nozzle and are connected individually via a control line to a current regulator. In accordance with another embodiment, groups of three electrodes are connected with a current regulator, which are in turn connected to a voltage source.
The German patent application DE 10 2007 024 090 A1 suggests a device for plasma treatment that includes several plasma generators. In housing of each plasma generator, acting as an external electrode, a nozzle opening is trained which houses an inner electrode. About a branch of a common gas supply of the device, a gas stream is fed into each plasma source.
Piezoelectric high-voltage generators are used in plasma sources as electrodes and are suitable for light the plasma from gases near atmospheric pressure, see for example, DE 10 2005 032 890 A1. However, they are limited in their performance by the thermal losses and its electromechanical limit. The power limit by the thermal losses can be overcome by an efficient transfer of heat to the environment, but their overall performance limited remains. This is accompanied by a reduced plasma power when compared to other types of plasma generators. A cluster of several such plasma generators is also possible, with which a sufficiently high plasma density over larger areas can be achieved.
With a nozzle like structure, the plasma density can be increased locally by a secondary plasma beam, which is produced with relatively high ion density. However, a large-scale treatment of a surface is possible a grid like scanning of the surface with the plasma beam. Apart from the mechanically complex additional scanning device the time to treat surfaces is thus significantly extended. The clusters described DE 10 2005 032 890 A1 allow a little variable and limited configurability of the system. Also, the electrical wiring and supply of process gas of the individual plasma generators and is time-consuming and expensive.